A thermoplastic elastomer composition obtained by dynamically heat-treating a rubber and a polyolefin-based resin in the presence of a crosslinking agent generally has a structure wherein the rubber component constitutes a soft segment. (soft phase) which imparts flexibility, the polyolefin-based resin constitutes a hard segment. (hard phase) which provides a pseudo crosslinked structure, and the phase composed of the soft segment (referred to as an “island phase” hereinafter) is dispersed in the phase composed of the hard segment (referred to as a “sea phase” hereinafter). Since the thermoplastic elastomer composition has such a structure, it can exhibit excellent mechanical properties such as rubber elasticity and tensile strength.
The thermoplastic elastomer composition is produced mainly by the use of a twin-screw extruder. However, when the twin-screw extruder is used, dispersing of the island phase is not necessarily sufficient, and therefore, a composition having excellent mechanical properties and appearance has not been obtained in many cases. For example, in patent literatures 1 to 4, a production process for a thermoplastic elastomer composition using a twin-screw extruder is disclosed. In the resulting thermoplastic elastomer composition, however, dispersibility of the island phase is not necessarily satisfactory, and development of a production process for a thermoplastic elastomer composition in which further improvement in dispersibility of the island phase is realized and which can produce a molded product having more excellent mechanical properties and appearance has been desired. A molded product is usually produced by extrusion molding, and from the viewpoint of production efficiency, higher extruder output is being desired.